Integrated circuit chips are being used now in all kinds of apparatus to provide complex electrical circuitry for controlling different operations or for providing data and mathematical calculations in business, education, science and many other fields. With successive advances in time, the size of the integrated circuit chips has progressively decreased, particularly because the thickness of the electrical leads in the chips has progressively decreased. Even as the chips have decreased in size, the circuitry on the chips has become progressively complex.
The integrated chips are formed in wafers, each of which holds a number, hundreds and often even thousands, of integrated circuit chips. The chips on the wafer are formed from a plurality of successive layers. Some of the layers provide electrical insulation. Others of the layers are electrically conductive. Electrical pegs or vias are provided between the different electrically conductive layers. The electrical pegs or vias are disposed in sockets provided in insulating layers in the chips. When the fabrication of the wafers has been completed, each chip defines electrical circuitry which performs specialized, often complex, operations.
The fabrication of the different layers in an integrated circuit chip has to be precise. For example, the width and thickness of the circuit leads in the different layers have to be precise in order to maintain the proper impedance values for different components in the circuits. If the proper impedance values are not maintained, the operation of the circuitry in the integrated circuit chip is impaired. Variations in the width and thickness of the circuit leads can result from impurities in the surfaces of different layers in the chips and from uneven and non-smooth surfaces on the insulating layers on which electrically conductive material is deposited. The criticality in maintaining surfaces even and smooth has increased as the thickness of the leads on the integrated circuit chips has decreased.
Apparatus has existed for a considerable number of years to etch the surfaces of different layers on the chips. The purpose of the etching has been to clean and refresh the surfaces to receive subsequent layers of deposition. The etching has produced uneven surfaces on the layers, thereby producing variations in the characteristics of the electrical material subsequently deposited on the uneven surfaces. The problem has been aggravated as the thickness of the layers has decreased. Attempts have been made to resolve this problem by making the etched surfaces even and uniform. The attempts have provided significant success but improvements in the smoothness and evenness of the surfaces of the insulating layer are constantly desired.